A massless scalar field without self-interaction and string coupled to grav
ity is quantized in the framework of quantum cosmology using the Bohm-de Br
oglie interpretation. Gaussian superpositions of the quantum solutions of t
he corresponding Wheeler-DeWitt equation in minisuperspace are constructed.
The Bohmian trajectories obtained exhibit a graceful exit from the inflati
onary pre-big, bang epoch to the decelerated expansion phase. (C) 2001 Else
vier Science B.V. All rights reserved.